Comparison of pharmacodynamics and pharmacokinetics of insulin degludec and insulin glargine 300 U/mL in healthy cats

Insulin glargine 300 U/mL (IGla-U300) and insulin degludec (IDeg) are synthetic insulin analogs designed as basal insulin formulations. In people, IGla-U300 is more predictable and longer acting compared with glargine 100 U/mL. The duration of action of IDeg in people is > 42 h, allowing flexibility in daily administration. We hypothesized that IDeg would have longer duration of action compared with IGla-U300 in healthy purpose-bred cats. Seven cats received 0.4 U/kg (subcutaneous) of IDeg and IGla-U300 on two different days, >1 wk apart. Exogenous insulin was measured and pharmacodynamic parameters were derived from glucose infusion rates during isoglycemic clamps and suppression of endogenous insulin. The Shapiro-Wilk test was used to assess normality, and normally distributed parameters were compared using paired t-tests. There was no difference between IDeg and IGla-U300 in onset, peak action, or total metabolic effect. On average, time to peak action (T_PEAK) of IGla-U300 was 145 ± 114 min (95% confidence interval [CI] = 25-264) longer than T_PEAK of IDeg (P = 0.03) and duration of action (T_DUR) of IGla-U300 was 250 ± 173 min (95% CI = 68-432) longer than T_DUR of IDeg (P = 0.02). The "flatness" of the time-action profile (as represented by the quotient of peak action/T_DUR) was significantly greater for IGla-U300 compared with IDeg (P = 0.04). Overall, insulin concentration measurements concurred with findings from isoglycemic clamps. Based on these data, IDeg is not suitable for once-daily administration in cats. The efficacy of once-daily IGla-U300 in diabetic cats should be further investigated.

Pharmacodynamics and pharmacokinetics of insulin aspart assessed by use of the isoglycemic clamp method in healthy cats

The objective of this study was to determine the pharmacodynamics (PD) and pharmacokinetics (PK) of insulin aspart in healthy cats following intramuscular (IM) and subcutaneous (SC) injection. Eight healthy, purpose-bred cats were used in a randomized, crossover study design. Each cat had 2 isoglycemic clamps performed, one after receiving 0.25 IU/kg of insulin aspart by IM injection and one after receiving the same dose by SC injection. The two isoglycemic clamps were performed on different days, at least 48 h apart. The blood glucose, plasma endogenous insulin, and plasma insulin aspart concentrations were measured and the glucose infusion rate (GIR) was recorded during the clamp. The GIR over time was used to create a time-action curve for each clamp which was used to describe the PD of insulin aspart. Data that are normally distributed are reported as mean ± SD, while data that are not normally distributed are reported as median (25-75 percentile). When compared to the PD data that have been reported for regular insulin in healthy cats, insulin aspart had a more rapid onset (IM: 10 min [10-21.25 min], SC: 12.5 min [10-18.75 min]) and shorter duration of action (IM: 182.5 ± 34.33 min, SC: 159.38 ± 41.87 min). The onset of action (P = 0.795), time to peak action (P = 0.499), duration of action (P = 0.301), and total metabolic effect (P = 0.603) did not differ with route of administration; however, SC administration did result in a higher maximum plasma insulin aspart concentration (IM: 1,265.17 pmol/L [999.69-1,433.89 pmol/L], SC: 3,278.19 pmol/L [2,485.29-4,132.01 pmol/L], P = 0.000) and larger area under the insulin aspart vs time curve (IM: 82,662 ± 30,565 pmol/L, SC: 135,060 ± 39,026 pmol/L, P = 0.010). Insulin aspart has a rapid onset of action and short duration of effect in healthy cats when administered by IM and SC injection. Although it cannot be assumed that the PD and PK of insulin aspart will be the same in cats with diabetic ketoacidosis (DKA), our data support further investigation into the use of SC insulin aspart as an alternative to regular insulin for the treatment of DKA in cats.

Estimating glucose requirements of an activated immune system in growing pigs

Activated immune cells become obligate glucose utilizers, and a large i.v. lipopolysaccharide (LPS) dose causes insulin resistance and severe hypoglycemia. Therefore, study objectives were to quantify the amount of glucose needed to maintain euglycemia following an endotoxin challenge as a proxy of leukocyte glucose requirements. Fifteen fasted crossbred gilts (30.3 ± 1.7 kg) were bilaterally jugular catheterized and assigned 1 of 2 i.v. bolus treatments: control (CON; 10 mL sterile saline; = 7) or LPS challenge + euglycemic clamp (LPS-Eu; 055:B5; 5 μg/kg BW; 50% dextrose infusion to maintain euglycemia; = 8). Following administration, blood glucose was determined every 10 min and dextrose infusion rates were adjusted in LPS-Eu pigs to maintain euglycemia for 8 h. Pigs were fasted for 8 h prior to the bolus and remained fasted throughout the challenge. Rectal temperature was increased in LPS-Eu pigs relative to CON pigs (39.8 vs. 38.8°C; < 0.01). Relative to the baseline, CON pigs had 20% decreased blood glucose from 300 to 480 min postbolus ( = 0.01) whereas circulating glucose content in LPS-Eu pigs did not differ ( = 0.96) from prebolus levels. A total of 116 ± 8 g of infused glucose was required to maintain euglycemia in LPS-Eu pigs. Relative to CON pigs, overall plasma insulin, blood urea nitrogen, β-hydroxybutrate, lactate, and LPS-binding protein were increased in LPS-Eu pigs (295, 108, 29, 133, and 13%, respectively; ≤ 0.04) whereas NEFA was decreased (66%; < 0.01). Neutrophils in LPS-Eu pigs were decreased 84% at 120 min postbolus and returned to CON levels by 480 min ( < 0.01). Overall, lymphocytes, monocytes, eosinophils, and basophils were decreased in LPS-Eu pigs relative to CON pigs (75, 87, 70, and 50%, respectively; ≤ 0.05). These alterations in metabolism and the large amount of glucose needed to maintain euglycemia indicate nutrient repartitioning away from growth toward the immune system. Glucose is an important fuel for the immune system, and data from this study established that the glucose requirements of an intensely and acutely activated immune system in growing pigs are approximately 1.1 g/kg BW/h.

Effects of diet-induced weight gain and turnout to pasture on insulin sensitivity in moderately insulin resistant horses

OBJECTIVE

To quantify insulin sensitivity and monitor glucose, insulin, and lipid concentrations in a group of moderately insulin-resistant horses during induction of obesity by use of a forage diet supplemented with fat and during subsequent turnout to pasture. ANIMALS 9 adult Standardbred mares (11 to 20 years old).

PROCEDURES

Weight gain of horses was induced during 22 weeks by use of a forage diet supplemented with fat fed in gradually increasing amounts, followed by feeding of that fat-supplemented diet at 2.5 times the daily maintenance requirements. Horses were then turned out to pasture. Insulin sensitivity was measured with the euglycemic hyperinsulinemic clamp method before and after weight gain and after 4 weeks at pasture. Body weight, body condition score, and cresty neck score as well as fasting and postprandial concentrations of plasma insulin, plasma glucose, serum triglyceride, and serum nonesterified fatty acids were measured during the study.

RESULTS

Body weight typically increased by 10%, and body condition score (scale, 1 to 9) increased by > 1.5 from the start to the end of the weight-gain period. There was no difference in insulin sensitivity or metabolic clearance rate of insulin during the weight-gain period. Four weeks at pasture generally improved insulin sensitivity and metabolic clearance rate of insulin by 54% and 32%, respectively, but there was no change in body weight or body condition score.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings indicated that dietary composition played a more important role than did short-term weight gain on alterations in insulin sensitivity of horses.

Validation of different measures of insulin sensitivity of glucose metabolism in dairy cows using the hyperinsulinemic euglycemic clamp test as the gold standard

The aim of the present research was to compare different measures of insulin sensitivity in dairy cows at the end of the dry period. To do so, 10 clinically healthy dairy cows with a varying body condition score were selected. By performing hyperinsulinemic euglycemic clamp (HEC) tests, we previously demonstrated a negative association between the insulin sensitivity and insulin responsiveness of glucose metabolism and the body condition score of these animals. In the same animals, other measures of insulin sensitivity were determined and the correlation with the HEC test, which is considered as the gold standard, was calculated. Measures derived from the intravenous glucose tolerance test (IVGTT) are based on the disappearance of glucose after an intravenous glucose bolus. Glucose concentrations during the IVGTT were used to calculate the area under the curve of glucose and the clearance rate of glucose. In addition, glucose and insulin data from the IVGTT were fitted in the minimal model to derive the insulin sensitivity parameter, Si. Based on blood samples taken before the start of the IVGTT, basal concentrations of glucose, insulin, NEFA, and β-hydroxybutyrate were determined and used to calculate surrogate indices for insulin sensitivity, such as the homeostasis model of insulin resistance, the quantitative insulin sensitivity check index, the revised quantitative insulin sensitivity check index and the revised quantitative insulin sensitivity check index including β-hydroxybutyrate. Correlation analysis revealed no association between the results obtained by the HEC test and any of the surrogate indices for insulin sensitivity. For the measures derived from the IVGTT, the area under the curve for the first 60 min of the test and the Si derived from the minimal model demonstrated good correlation with the gold standard.

Effects of the rate of insulin infusion during isoglycemic, hyperinsulinemic clamp procedures on measures of insulin action in healthy, mature thoroughbred mares

The objective of this study was to determine whether the rate of insulin infusion during isoglycemic hyperinsulinemic clamp procedures affected measures of insulin action, including glucose disposal and plasma non-esterified fatty acid, endothelin-1, and nitric oxide concentrations, in mature, healthy horses. Eight thoroughbred mares were studied during a 2-h hyperinsulinemic clamp procedure, conducted at each of 4 rates of insulin infusion: 0 (CON), 1.2 (LOWINS), 3 (MEDINS), and 6 (HIGHINS) mU · kg(-1) · min(-1). The infusion rate of a dextrose solution was adjusted throughout the clamp procedures to maintain blood glucose levels within 10% of baseline glucose concentrations. Plasma insulin concentrations were measured throughout the clamp procedures, and used with the rate of glucose infusion to calculate the plasma insulin concentration-to-rate of glucose infusion ratio, a measure of insulin action on glucose disposal. The rate of glucose infusion increased with rate of insulin infusion (P < 0.05). The plasma insulin concentration-to-rate of glucose infusion ratio was highest for the LOWINS treatment (P < 0.05) and decreased by 62% (P < 0.05) and 84% (P < 0.05) for the MEDINS and HIGHINS treatments, respectively. Although plasma non-esterified fatty acid concentrations were lower than baseline by t = 30 min of the clamp procedures in the LOWINS, MEDINS, and HIGHINS treatments (P < 0.05), the decline was similar for all 3 rates of insulin infusion. Jugular vein plasma nitric oxide and endothelin-1 concentrations were not affected by insulin infusion rate (P > 0.05). The data indicate that it is important to standardize insulin infusion rate if data are to be compared between hyperinsulinemic clamp studies.

The GLP-1 mimetic exenatide potentiates insulin secretion in healthy cats

The glucagon-like peptide-1 mimetic exenatide has a glucose-dependent insulinotropic effect, and it is effective in controlling blood glucose (BG) with minimal side effects in people with type 2 diabetes. Exenatide also delays gastric emptying, increases satiety, and improves β-cell function. We studied the effect of exenatide on insulin secretion during euglycemia and hyperglycemia in cats. Nine young, healthy, neutered, purpose-bred cats were used in a randomized, cross-over design. BG concentrations during an oral glucose tolerance test were determined in these cats previously. Two isoglycemic glucose clamps (mimicking the BG concentration during the oral glucose tolerance test) were performed in each cat on separate days, one without prior treatment (IGC) and the second with exenatide (1 μg/kg) injected subcutaneously 2 h before (ExIGC). BG, insulin, and exenatide concentrations were measured, and glucose infusion rates were recorded and compared in paired tests between the two experiments. After exenatide injection, insulin serum concentrations increased significantly (2.4-fold; range 1.0- to 9.2-fold; P = 0.004) within 15 min. This was followed by a mild decrease in BG concentration and a return of insulin concentration to baseline despite a continuous increase in serum exenatide concentrations. Insulin area under the curve (AUC) during ExIGC was significantly higher than insulin AUC during IGC (AUC ratio, 2.0 ± 0.4; P = 0.03). Total glucose infused was not significantly different between IGC and ExIGC. Exenatide was detectable in plasma at 15 min after injection. The mean exenatide concentration peaked at 45 min and then returned to baseline by 75 min. Exenatide was still detectable in the serum of three of five cats 8 h after injection. No adverse reactions to exenatide were observed. In conclusion, exenatide affects insulin secretion in cats in a glucose-dependent manner, similar to its effect in other species. Although this effect was not accompanied by a greater ability to dispose of an intravenous glucose infusion, other potentially beneficial effects of exenatide on pancreatic β cells, mainly increasing their proliferation and survival, should be investigated in cats.

The effect of long-term exercise on glucose metabolism and peripheral insulin sensitivity in Standardbred horses

REASONS FOR PERFORMING STUDY

To study the possible long-term effect of improved glucose tolerance in horses after long-term training, as the impact of exercise training on glucose metabolism is still unclear in the equine species. It is not known whether there is a direct long-term effect of training or if the measurable effect on glucose metabolism is the residual effect of the last exercise session.

OBJECTIVES

To determine the chronic effect on glucose metabolism and peripheral insulin sensitivity of long-term training in horses by use of the euglycaemic hyperinsulinaemic clamp technique.

METHODS

Eleven Standardbred horses were acclimatised to running on the high-speed treadmill for 4 weeks (Phase 1) followed by training for 18 weeks with an alternating endurance (approximately 60% HRmax) high intensity training programme (approximately 80% HRmax) (Phase 2). Training frequency was 4 days/week. At the end of Phase 1, a euglycaemic hyperinsulinaemic clamp was performed 72 h after the last bout of exercise in all horses. At the end of Phase 2, the horses were clamped 24 h or 72 h after the last bout of exercise.

RESULTS

Glucose metabolism rate did not change significantly after 18 weeks of training, measured 72 h after the last exercise bout (0.018 +/- 0.009 and 0.022 +/- 0.006 mmol/kg bwt/min, respectively). Peripheral insulin sensitivity also did not change significantly following training (7.6 +/- 5.7 x 10(-6) and 8.0 +/- 3.1 x 10(-6), respectively). The same measurements 24 h after the last bout of exercise showed no significant differences.

CONCLUSIONS

Results indicated that long-term training in Standardbreds neither changed glucose metabolism or insulin sensitivity 72 h after the last bout of exercise.

POTENTIAL RELEVANCE

The fact that the beneficial effect of increased insulin sensitivity after acute exercise diminishes quickly in horses and no long-term effects on insulin sensitivity after chronic exercise have as yet been found in horses, implies that exercise should be performed on a regular basis in horses to retain the beneficial effect of improved insulin sensitivity.

Effects of prior exercise on components of insulin signalling in equine skeletal muscle

REASONS FOR PERFORMING STUDY

Exercise is an important stimulus for the regulation of numerous metabolic functions in muscle, but there has been little investigation of the mechanism of exercise-enhanced glucose utilisation.

OBJECTIVE

To examine the effects of exercise on the signalling components Akt and glycogen synthase kinase-3 (GSK3) involved in insulin regulation of glycogen synthase (GS) activity. It was hypothesised that hyperinsulinaemia and prior exercise would alter the extent of Akt phosphorylation and GSK3beta deactivation and increase insulin stimulation of GS activity in skeletal muscle.

METHODS

Eight Standardbred horses completed a euglycaemic-hyperinsulinaemic clamp (EHC) either without prior exercise (NonEX) or at 0.5, 4 or 24 h post exercise (0.5 PostEX, 4 PostEX, and 24 PostEX, respectively). Muscle samples for determination of Akt and GSK3 serine phosphorylation, and GS fractional velocity (GS(FV)) were collected 5 min before (Pre-INS) and at the end (Post-INS) of each EHC (pre- and post insulin stimulation). Protein was separated by SDS-PAGE on polyacrylamide gels, transferred to nitrocellulose membranes and incubated with antibodies against phospho-Akt Ser473 and GSK3alpha/beta Ser21/9.

RESULTS

GS(FV) was increased (P<0.05) 2-fold at 0.5 PostEX, 4 PostEX and 24 PostEX when compared to NonEX in Pre-INS and in Post-INS was increased 33 and 28% in NonEX and at 24PostEX (P<0.05), respectively, when compared to Pre-INS in these trials. Phospho-Akt Ser473 was increased at 0.5 PostEX only (P<0.05) in Pre-INS but increased in all trials in Post-INS. Phospho-GSK3alpha (Ser21) was also greater (P<0.05) at 0.5 PostEX in Pre-INS than in NonEX and 24 PostEX and in Post-INS increased (P<0.05) in NonEX and at 24 PostEX but not at 0.5 PostEX or 4 PostEX post exercise. There was no effect of time or treatment on GSK3, (Ser9) phosphorylation or on total GSK3.

CONCLUSIONS

Elevated plasma insulin and prior exercise were associated with Akt activation and GSK3alpha deactivation (0.5 PostEX) indicating that an effect of exercise is evident in the early post exercise period and supporting a physiological role for GSK3alpha in the regulation of GS activity. The changes are consistent with insulin signalling downstream from these molecules.

Effects of short-term training on insulin sensitivity and skeletal muscle glucose metabolism in Standardbred horses

REASONS FOR PERFORMING STUDY

Increased insulin sensitivity occurs after a period of exercise training, but the mechanisms underlying this training-associated increase in insulin action have not been investigated.

OBJECTIVE

To examine the effects of short-term endurance training (7 consecutive days) and a subsequent period of inactivity (5 days) on whole body insulin sensitivity and GLUT-4 protein and the activities of glycogen synthase (GS) and hexokinase (HK) in skeletal muscle. It was hypothesised that training would increase insulin sensitivity in association with increased GLUT-4 protein and activities of GS and HK, but that these changes would be transient, returning to baseline after 5 days of inactivity.

METHODS

Seven mature Standardbred horses completed training consisting of 7 consecutive days of 45 min of treadmill exercise at a speed that elicited 55% of pretraining maximal aerobic capacity (VO2peak). Insulin sensitivity was determined by rate of glucose disposal (M) during the last 60 min of a 120 min euglycaemic-hyperinsulinaemic clamp (EHC) performed before (-2 days) and at 1 and 6 days following training. VO2peak was measured before (UT) and after (TR) training and the period of inactivity (IA).

RESULTS

Training resulted in a 9% increase in mean VO2peak (P<0.05) that was maintained following inactivity (IA). Mean M values were more than 2-fold higher (P<0.05) in TR than in UT. Mean M was also higher (P<0.05) in IA when compared to UT. GLUT-4 protien abundancewas more than 10-fold higher in TR and IA (P<0.001) than in UT. Pre-EHC GS activity and GS fractional velocity were increased (P<0.05) in TR when compared to UT and IA. Pre-EHC HK activity was increased (P<0.05) in IA when compared to UT and TR. Muscle glycogen was 66% lower (P<0.05) in TR than in UT and IA.

CONCLUSIONS

Short-term training resulted in increases in whole body insulin sensitivity, and GLUT-4 protein content and glycogen synthase activity in skeletal muscle. The enhancements in insulin sensitivity, GLUT-4 protein and glycogen synthase activity were still evident after 5 days of inactivity.

POTENTIAL RELEVANCE

Insulin resistance in equids has been associated with obesity and predisposition to laminitis. Regular physical activity may mitigate risk of these conditions via enhancement of insulin sensitivity and/or control of bodyweight.

Short communication: Regulation of milk fat yield and fatty acid composition by insulin

Diet-induced milk fat depression in dairy cows has been known for many years and several theories have been proposed. One that continues to receive support is the glucogenic-insulin theory. Previous studies testing this theory using a hyperinsulinemic-euglycemic clamp have had variable results attributable to variability in the use of body fat reserves as a source of milk fatty acids. Our objective was to test the glucogenic-insulin theory using cows immediately postpartum, a period when the use of body fat for milk fat synthesis is greatest. During wk 2 postpartum, 5 cows were given a 2-d baseline period and then clamped for 4 d. Insulin was increased more than 2-fold during the clamp while the blood glucose concentration was maintained. Milk yield was not altered by administration of the clamp (38.7 vs. 39.0 +/- 1.4 kg/d); however, the milk fat percentage and yield were reduced by 27% and plasma nonesterified fatty acids were reduced by 68%. Analysis of the milk fatty acid composition revealed that the decrease in milk fat yield during use of the clamp was almost exclusively due to reductions in preformed fatty acids; this is the exact opposite of what is observed with diet-induced milk fat depression. Therefore, our results do not support the glucogenic-insulin theory of diet-induced milk fat depression. The results further indicated that reductions in milk fat observed previously with hyperinsulinemic-euglycemic clamps or with glucose or propionate infusions were most likely consequences of the ability of insulin to inhibit lipolysis, thereby limiting the mammary availability of preformed fatty acids mobilized from body reserves.

Factors affecting clinical assessment of insulin sensitivity in horses

Insulin resistance is thought to be involved in the pathogenesis of many equine conditions such as pars intermedia dysfunction, equine metabolic syndrome, diabetes mellitus, hyperlipaemia, laminitis, endotoxaemia and osteochondrosis dissecans (OCD); whereas polysaccharide storage myopathy in Quarter Horses and equine motor neuron disease (EMD) have been associated with increased insulin sensitivity. However, it is clear that there is not one ideal test, in terms of both practicality and accuracy, for evaluating insulin sensitivity in horses and improved diagnostic techniques are required. This review sets out the background to the subject and identifies current knowledge regarding the measurement of insulin sensitivity by tolerance testing and clamping techniques. Factors affecting insulin sensitivity, such as breed, pregnancy, lactation, obesity and nutritional factors are discussed. In addition, the relationship with training, nutritional supplementation and drug administration are considered.

Effects of dietary energy source and physical conditioning on insulin sensitivity and glucose tolerance in standardbred horses

REASONS FOR PERFORMING STUDY

There is evidence that adaptation to diets rich in nonstructural carbohydrates (NSC) contributes to the development of insulin resistance in horses. To date, however, no study in horses has examined the effects of physical conditioning on diet-associated alterations in insulin sensitivity and glucose tolerance.

OBJECTIVES

To examine the effects of adaptation to concentrate feeds rich in NSC or fat on insulin sensitivity and glucose tolerance in horses, both in the sedentary state and after a subsequent period of physical conditioning.

METHODS

Fourteen mature Standardbred horses underwent both a euglycaemic-hyperinsulinaemic clamp (EHC) and oral glucose tolerance test (OGTT) after each of the following phases: Baseline - fed only forage cubes for 3 weeks; Diet horses were randomly assigned to receive either a high NSC (S) concentrate or a high fat concentrate (F) with forage cubes for 6 weeks; and Diet x Exercise - horses remained on the assigned ration and underwent a 7 week period of physical conditioning. An incremental exercise test was performed before, and after, the Diet x Exercise phase for measurement of the peak rate of oxygen consumption (VO2peak).

RESULTS

In both diet groups, there was an approximately 10% increase in mean VO2peak after physical conditioning. The mean rate of glucose disposal (M) per unit of serum insulin (I) during the EHC [M/I ratio] in S horses was 30% lower (P<0.05) in the Diet phase when compared to Baseline, but not different from Baseline after physical conditioning. The S diet also resulted in a greater (P<0.05) OGTT insulin response (area under the insulin vs. time curve, AUC(INS)) in both Diet and Diet x Exercise phases when compared to Baseline. In F, insulin sensitivity (mean M/I ratio) and glucose tolerance were unchanged during the study.

CONCLUSIONS AND POTENTIAL RELEVANCE

Feeding a diet rich in NSC for 6 weeks resulted in decreased insulin sensitivity and impaired glucose tolerance. Physical conditioning lessened the effects of the high NSC diet on insulin sensitivity, as evidenced by the return to baseline M/I, but did not mitigate the impaired glucose tolerance. Decreased insulin sensitivity has been implicated in the development of obesity and laminitis in horses and the present findings provide support for avoidance of concentrates with high NSC in the dietary management of horses at risk for the development of these conditions.

Effects of colostrum feeding and glucocorticoid administration on insulin-dependent glucose metabolism in neonatal calves

Colostrum feeding and glucocorticoid administration affect glucose metabolism and insulin release in calves. We have tested the hypothesis that dexamethasone as well as colostrum feeding influence insulin-dependent glucose metabolism in neonatal calves using the euglycemic-hyperinsulinemic clamp technique. Newborn calves were fed either colostrum or a milk-based formula (n=14 per group) and in each feeding group, half of the calves were treated with dexamethasone (30 microg/[kg body weight per day]). Preprandial blood samples were taken on days 1, 2, and 4. On day 5, insulin was infused for 3h and plasma glucose concentrations were kept at 5 mmol/L+/-10%. Clamps were combined with [(13)C]-bicarbonate and [6,6-(2)H]-glucose infusions for 5.5h (i.e., from -150 to 180 min, relative to insulin infusion) to determine glucose turnover, glucose appearance rate (Ra), endogenous glucose production (eGP), and gluconeogenesis before and at the end of the clamp. After the clamp liver biopsies were taken to measure mRNA levels of phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC). Dexamethasone increased plasma glucose, insulin, and glucagon concentrations in the pre-clamp period thus necessitating a reduction in the rate of glucose infusion to maintain euglycemia during the clamp. Glucose turnover and Ra increased during the clamp and were lower at the end of the clamp in dexamethasone-treated calves. Dexamethasone treatment did not affect basal gluconeogenesis or eGP. At the end of the clamp, dexamethasone reduced eGP and PC mRNA levels, whereas mitochondrial PEPCK mRNA levels increased. In conclusion, insulin increased glucose turnover and dexamethasone impaired insulin-dependent glucose metabolism, and this was independent of different feeding.

Active immunization against leptin fails to affect reproduction and exerts only marginal effects on glucose metabolism in young female goats

Approximately 150 days before expected breeding time, 12 female goats (3 months of age) were actively immunized against ovine leptin. Booster injections were given throughout the following year. Control animals (n = 6) were sham-immunized. After the first observed oestrus, a buck was introduced and goats were mated. Blood samples were collected twice weekly and frequent blood sampling series were performed on days -15, 76, 153 and 286 relative to the first immunization. Nine of the immunized goats developed titres within 3 months and had elevated serum concentrations of leptin compared with controls (p < 0.0001). Hematological parameters and blood chemistry were not affected by the immunization. No differences were detectable in all reproductive parameters recorded. Serum insulin was higher in immunized goats during the frequent blood sampling series of day 287 after the first immunization. Glucose metabolism was investigated during pregnancy using hyperglycaemic and euglycaemic/hyperinsulinaemic clamps. None of the parameters derived from the clamp studies was different (p > 0.05) between the two groups. During the hyperglycaemic clamp there was a trend (p < 0.15) towards increased insulin concentrations in immunized animals whereas glucose infusion rates were not different between the groups. This indicates decreased insulin sensitivity in immunized goats. Our study describes the ontogenesis of serum concentrations of leptin during growth, puberty and first pregnancy and parturition for the caprine species. The effects of the immunization were not detectable or only marginal and the approach aimed at therefore not effective to investigate leptin action in detail.

Repeatability of 2 methods for assessment of insulin sensitivity and glucose dynamics in horses

Both the euglycemic-hyperinsulinemic clamp (EHC) and minimal model analysis of the frequently sampled intravenous glucose tolerance test (FSIGT) have been applied for measurement of insulin sensitivity in horses. However, no published data are available on the reproducibility of these methods. Therefore, the objective of this study was to evaluate the variation and repeatability of measures of glucose dynamics and insulin sensitivity in horses derived from minimal model analysis of the FSIGT and from the EHC method. Six healthy horses underwent both the FSIGT and EHC on 2 occasions over a 4-week period, with a minimum of 5 days between tests. Coefficient of variation (CV) and intraclass correlation coefficient (ICC) were calculated for measures of glucose metabolism and insulin sensitivity derived from each test. In the EHC, insulin sensitivity, expressed as the amount of metabolized glucose (M) per unit of serum insulin (I) (M/I ratio), averaged 0.19 +/- 0.06 x 10(-4) mmol/kg/min x (pmol/L)(-1) with an average interday CV of 14.1 +/- 5.7% (range, 7-20%) and ICC of 0.74. Minimal model analysis of the FSIGT demonstrated mean insulin sensitivity (Si) of 0.49 +/- 0.17 x 10(-4)/min x (pmol/L)(-1) with an average interday CV of 23.7 +/- 11.2% (range, 9-35%) and ICC of 0.33. Mean CV and ICC for minimal model glucose effectiveness (Sg) and acute insulin response (AIRg) were, respectively, 26.4 +/- 11.2% (range 13-40%) and 0.10 and 11.7 +/- 6.5% (range 7-21%) and 0.98. Insulin sensitivity measured by the EHC has lower interday variation when compared with the minimal model estimate derived from the FSIGT.

Effects of short- and long-term recombinant equine growth hormone and short-term hydrocortisone administration on tissue sensitivity to insulin in horses

OBJECTIVE

To determine the effects of short-term IV administration of hydrocortisone or equine growth hormone (eGH) or long-term IM administration of eGH to horses on tissue sensitivity to exogenous insulin.

ANIMALS

5 Standardbreds and 4 Dutch Warmblood horses.

PROCEDURE

The euglycemic-hyperinsulinemic clamp technique was used to examine sensitivity of peripheral tissues to exogenous insulin 24 hours after administration of a single dose of hydrocortisone (0.06 mg/kg), eGH (20 microg/kg), or saline (0.9% NaCl) solution and after long-term administration (11 to 15 days) of eGH to horses. The amounts of metabolized glucose (M) and plasma insulin concentration (I) were determined.

RESULTS

Values for M and the M-to-I ratio were significantly higher 24 hours after administration of a single dose of hydrocortisone than after single-dose administration of eGH or saline solution. After long-term administration of eGH, basal I concentration was increased and the mean M-to-I ratio was 22% lower, compared with values for horses treated with saline solution.

CONCLUSIONS AND CLINICAL RELEVANCE

Increases in M and the M-to-I ratio after a single dose of hydrocortisone imply that short-term hydrocortisone treatment increases glucose use by, and insulin sensitivity of, peripheral tissues. Assuming a single dose of hydrocortisone improves sensitivity of peripheral tissues to insulin, it may be an interesting candidate for use in reducing insulin resistance in peripheral tissues of horses with several disease states. In contrast, long-term administration of eGH decreased tissue sensitivity to exogenous insulin associated with hyperinsulinemia. Therefore, increased concentrations of growth hormone may contribute to insulin resistance in horses with various disease states.

Evaluation of glucose metabolism in three horses with lower motor neuron degeneration

OBJECTIVES

To determine whether increased glucose metabolism is the potential cause of the decreased plasma glucose curve determined after oral glucose tolerance testing in horses with lower motor neuron degeneration.

ANIMALS

3 horses with signs suggestive of lower motor neuron degeneration, 1 horse with malignant melanoma with multiple metastases, and an obese but otherwise healthy horse. Procedures-Glucose metabolism was assessed by use of the hyperglycemic clamp and euglycemic hyperinsulinemic clamp techniques.

RESULTS

Mean rate of glucose metabolism of horses with lower motor neuron degeneration was significantly greater (mean, 3.7 times greater than control horses; range, 2.1 to 4.8 times greater) than that reported in 5 healthy control horses (41 +/- 13 micromol/kg/min vs 11 +/- 4.5 micromol/kg/min, respectively). In addition, one of the affected horses, an 8-year-old warmblood gelding, had a 5.6-times increased sensitivity to exogenously administered insulin, compared with that reported in 5 healthy control horses. Pancreatic insulin secretion was not insufficient in horses with lower motor neuron degeneration. Findings in the 2 diseased control horses were unremarkable.

CONCLUSIONS AND CLINICAL RELEVANCE

Increased glucose metabolism in horses with lower motor neuron degeneration may be the cause of the decreased plasma glucose curve detected after oral glucose tolerance testing. This finding could aid in developing supportive treatments with respect to adequate glucose and vitamin E supplementation.

Development of a model for inducing transient insulin resistance in the mare: preliminary implications regarding the estrous cycle

Peripheral insulin resistance is the failure of proper cellular glucose uptake in response to insulin. Insulin resistance and hyperinsulinemia are associated with several disease states in the horse and reproductive function disturbances in humans, including polycystic ovarian syndrome. To test the hypothesis that insulin resistance (IR) and hyperinsulinemia disrupt the estrous cycle in mares, two experiments were conducted to first develop a model to induce IR and to then examine the effect of this model on the duration of the estrous cycle. In Exp. 1, a hyperinsulinemic-euglycemic clamp (HEC) procedure was performed on seven mares to determine insulin sensitivity before and immediately following infusion of a heparinized lipid solution. The HEC procedure was repeated 1 wk after lipid infusion. Mares developed IR following the lipid infusion (P < 0.05), and some individuals maintained IR for up to 1 wk. Mares also exhibited increased blood insulin both immediately following treatment and 1 wk later (P < 0.05). In Exp. 2, induction of insulin resistance by lipid solution was not accompanied by changes in circulating concentrations of luteinizing hormone, and duration of the luteal phase, compared with the duration of untreated luteal phases. Nonetheless, lipid infusion and the resultant insulin resistance were associated with an increased interovulatory period (P < 0.05), and peak concentrations of progesterone (P < 0.05) were higher during the treated vs. untreated luteal phases of the estrous cycle. The results from the preliminary study suggest that infusion of a lipid solution may induce transient insulin resistance and hyperinsulinemia. The resulting insulin resistance and hyperinsulinemia may modify characteristics of the estrous cycle, perhaps at the level of the ovary.

Insulin resistance and changes in plasma concentration of TNFalpha, IGF1, and NEFA in dogs during weight gain and obesity

Obesity-induced insulin resistance (IR) is a common problem in humans as well as domestic dogs. It is well-known that this syndrome is associated with many modifications but it is still unclear if the changes are alterations or adaptations. The purpose of this study was to develop obesity-induced IR in dogs, through a long-term overfeeding period, and to explore hormonal and metabolic disturbances associated with the development of this syndrome. Dogs were overfed for 7 months. Body weight increased by 43 +/- 5%, and insulin sensitivity decreased by 44 +/- 5%. Plasma insulin-like growth factor 1 (IGF1), tumour necrosis factor alpha (TNFalpha), and non-esterified fatty acids (NEFA) concentrations progressively increased during the overfeeding period (IGF1: 111 +/- 13 to 266 +/- 32 ng/ml, p < 0.001; TNFalpha: 5 +/- 5 to 134 +/- 41 pg/ml; NEFA: 0.974 +/- 0.094 to 1.590 +/- 0.127 mmol/l, p < 0.05). These metabolic and hormonal impairments are associated with IR, in obese dogs, and could explain, at least in part, the outbreak of this syndrome.

The housekeeping genes GAPDH and cyclophilin are regulated by metabolic state in the liver of dairy cows

Steady-state levels of mRNA are often used to infer treatment effects on the levels of the corresponding protein. In addition, an internal standard RNA is usually measured to document specificity of treatment and to correct for intersample variation. Our objective was to evaluate whether glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and cyclophilin could be used as internal standards when studying changes in hepatic gene expression in dairy cows. Hepatic expression of GAPDH and cyclophilin was measured in 6 cows in late pregnancy (28 d prepartum) and early lactation (10 d postpartum). Each gene displayed 2- to 3-fold higher expression in early lactation than in late pregnancy. Next, we determined whether negative energy balance alone or in combination with exogenous growth hormone could mimic the effects of early lactation. Late-lactating cows were fed 120% of predicted energy requirements or 33% of maintenance requirements. During each feeding period, cows were administered excipient or bovine somatotropin in a single-reversal design with 4-d periods separated by a 2-d interval. Underfeeding increased hepatic expression of GAPDH and cyclophilin by 1- to 2-fold, whereas bovine somatotropin had no effect. Finally, the effects of insulin were studied by performing hyperinsulinemic-euglycemic clamps in late pregnancy (28 d prepartum) and early lactation (28 d postpartum). Hyperinsulinemia reduced GAPDH expression in both states, and cyclophilin expression in early lactation. In conclusion, GAPDH and cyclophilin are regulated in the liver of dairy cows and should not be used to standardize hepatic gene expression in studies involving the transition period, undernutrition, and sustained changes in plasma insulin.

Effect of short-term exercise training on insulin sensitivity in obese and lean mares

Twelve untrained aged mares were used to determine whether 7 days of light exercise improved peripheral tissue insulin sensitivity. Mares were divided into obese-exercised (n = 3), obese-sedentary (n = 3), lean-exercised (n = 3) and lean-sedentary (n = 3) groups. The exercised groups were worked at a trot to a heart rate (HR) of not more than 140 beats/min for 30 min in a round pen. Each group was subjected to 3 euglycaemic hyperinsulinaemic clamps: prior to exercise (P), 24 h following the seventh exercise training session (E) and 9 days postexercise training (PE). Prior to exercise training, the mares in the obese group were confirmed insulin-resistant compared to the mares in the lean group. There was no change in bodyweight or body condition in the obese or lean groups throughout the study. Glucose infusion rate (GIR) was higher (P<0.05) on E compared to P days in the obese-exercised and lean-exercised groups. Insulin sensitivity returned to pre-exercise values by 9 days postexercise in the obese-exercised and lean-exercised groups. The results of this study suggest that improvement in insulin sensitivity occurs in obese mares without a long interval of exercise training and in the absence of a change in bodyweight.

Protein metabolism in lactating goats subjected to the insulin clamp

A model of Leu and protein metabolism by the mammary gland and hind leg of lactating goats was constructed and evaluated from data collected by using [15N, 1-13C]Leu kinetics measured during amino acid (AA) infusion and a hyperinsulinemic-euglycemic clamp (IC). Goats were given continuous intravenous infusions of either saline or AA (65 g/d) for 7.5 d and from d 5 to 7.5 goats were subjected to IC. Arteriovenous kinetics were monitored on d 4 and 8 by continuous infusion (8 h) of [15N, 1-13C]Leu. Milk protein yield was increased by IC (+10%) and IC +AA (+21%), whereas AA infusion had no effect. The data were used to construct model equations that describe rates of protein synthesis and degradation, and from these equations, milk and muscle net protein synthesis were described. The model was unable to describe the observed responses in milk protein synthesis. Similar to observations in the literature, net protein gain by the hind leg increased with AA, IC, and IC + AA infusion, primarily through stimulation of protein synthesis by AA. For both tissues, IC depressed Leu oxidation, but only in the absence of AA infusion. Although the IC appears to regulate the ability of the mammary gland to coordinate blood flow and Leu catabolism in support of protein synthesis, our ability to construct a precise model describing mammary protein anabolism is still limited. In contrast, the response in protein anabolism of the hind-leg tissues of these midlactation goats was predicted well by the model, which indicate that the leg tissues were more sensitive to AA supply than the mammary gland.

Effects of hyperinsulinaemia under euglycaemic condition on liver fat metabolism in dairy cows in early and mid-lactation

The objective was to examine the effects of insulin under euglycaemic conditions on liver long chain fatty acids (LCFA) metabolism with special focus on the aetiology of hepatic lipidosis in early lactation. A 4-day hyperinsulinaemic-euglycaemic clamp (clamp) was conducted on four dairy cows starting in weeks 4 and 17 postpartum. Insulin was infused continuously (1 microg/kg BW per h) and a 50% glucose solution was infused to maintain euglycaemia. Liver biopsies were taken 6 days before, the last day of, and 5 days after the clamp, and blood samples were taken in the same period. In the liver tissue, the relative triglyceride content decreased (P < 0.01) and the glycogen content increased (P < 0.0001) in response to the clamp. Hepatic in vitro palmitate oxidation capacity was lowest during the clamp period and could be explained by a significant decrease in incomplete oxidation (ketogenesis) (P < 0.04) and a tendency to a decreased complete oxidation of palmitate (P < 0.10). Plasma non-esterified fatty acids concentration was decreased during the clamp in early lactation (P < 0.05) but there was no effect on the mid-lactation clamp. The present study shows that increased insulin under euglycaemic conditions seems to depress hepatic LCFA oxidation capacity. However, in terms of preventing hepatic lipidosis, the anti-lipolytic effect of insulin on adipose tissue, which results in decreased mobilization of and hence hepatic load with LCFA, appears more important.

Insulin sensitivity of heifers on different diets

The hyperinsulinemic euglycemic clamp technique was used to investigate the effect on insulin sensitivity of 2 different diets used in practical cattle feeding in calves. Ten 4 to 5-month-old heifer calves were allocated to 2 feeding groups, LO or HI, to obtain growth rates of 400 g/day or 900 g/day. The heifers were fed and housed individually for 5 weeks. Growth rates close to calculated rates were obtained with the diets used. Weekly blood samples were collected from the jugular vein for analysis of glucose, insulin, cortisol, total serum protein, urea, cholesterol and non-esterified fatty acids. During week 5, insulin sensitivity was estimated using the hyperinsulinemic euglycemic clamp technique. Insulin sensitivity did not differ between the groups, but the plasma glucose levels were higher during weeks 3 and 4 for the HI group compared to the LO group. It may be concluded that the amount of concentrate in the diet was too low to induce changes in either the basal plasma insulin levels or the insulin sensitivity in the HI group.

The effect of the plasma glucose level on the abomasal function in dairy cows

We have studied the effect of plasma glucose level on the abomasal outflow rate of fluid using a hyperinsulinemic glucose clamp technique in dairy cows. Four nonpregnant, nonlactating cows were subjected to one of the following treatments: hyperinsulinemic normoglycemic clamp; hyperinsulinemic hypoglycemic clamp; hyperinsulinemic hyperglycemic clamp; or, as a control, an intravenous infusion of .9% sodium chloride in a Latin square design. The cows were previously fitted with a permanent fistula in the abomasum and the outflow rate of abomasal fluid was determined using Co-EDTA as a marker assuming that the outflow followed first-order kinetics. The abomasal pH was also registered. Insulin was infused continuously through a jugular catheter at a rate of 4.8 mU. kg(-1)min(-1) for 2.5 h in the three clamp treatments. A glucose solution was infused through the catheter at a variable rate to achieve a circulating concentration, near the preinfusion glucose level (approximately 4.1 mmol/L), 2 mmol/L below the preinfusion level, and 2 mmol/L above the preinfusion level for the three hyperinsulinemic treatments, respectively. There was a significant effect of treatment on the rate of abomasal outflow (P < .001). The rate of abomasal outflow was highest for the control treatment (7.8%/min). The slowest outflow was observed in the hyperglycemic cows (3.40%/min). The hypoglycemic and normoglycemic cows showed intermediate rates (6.0%/min and 5.2%/min, respectively). The rate of outflow for the hyperglycemic cows was significantly lower than for all the other treatments (P < .01). Abomasal pH was affected by treatment (P < .05). The highest pH was observed in the hyperglycemic cows (pH 2.3). The values for the other three treatments ranged from pH 1.9 to 2.0. These results show that hyperglycemia reduced the rate of outflow and increased the pH of abomasal fluid in dairy cows. An elevated plasma glucose level thus can be considered as a potential risk factor in the pathogenesis of left-displaced abomasum.

Insulin-dependent whole-body glucose utilization and insulin-responses to glucose in week 9 and week 19 of lactation in dairy cows fed rumen-protected crystalline fat or free fatty acids

Whole-body insulin-dependent glucose utilization and insulin responses to glucose in euglycemic-hyperinsulinemic clamps (EHGC) and in hyperglycemic clamps (HGC) were evaluated in high yielding dairy cows fed rumen-protected fat (triglycerides), free fatty acids, or a starch-rich ration (n = 5 per group) in Week 9 and Week 19 of lactation. The experiment was performed under conditions of nonsignificant differences in energy and protein balances in Week 9 and Week 19 and in the three groups. Basal (pre-infusion) concentrations of glucose were lower (P < 0.05) in Week 9 than in Week 19 of lactation and were higher (P < 0.05) in Week 9 in cows fed free fatty acids than in cows fed the starch-rich ration. In EHGC, glucose infusion rates were similar in Week 9 and Week 19 and in the different groups, indicating similar insulin-dependent glucose utilization. Furthermore, because insulin concentrations in EHGC in Week 9 and Week 19 and in the three groups were very similar, metabolic clearance rates of insulin were not affected by stage of lactation and feeding. In addition, insulin responses to the same glucose increments in HGC were not different in Week 9 and Week 19 and in the three groups, indicating that insulin secretion was not affected by stage of lactation and feeding. In conclusion, insulin secretion, insulin metabolic clearance rate, and insulin-dependent glucose utilization between Week 9 and Week 19 of lactation were stable. Furthermore, feeding rumen-protected triglycerides or free fatty acids did not significantly modify insulin secretion, insulin metabolic clearance rate and glucose-dependent glucose utilization compared with starch-rich feeding.

Assessing insulin sensitivity in the cat: evaluation of the hyperinsulinemic euglycemic clamp and the minimal model analysis

Current methods of assessing glucose tolerance in the cat are inadequate for quantifying insulin sensitivity. The hyperinsulinemic euglycemic clamp (EGC) and the minimal model analysis (MMA) of the frequently sampled intravenous glucose tolerance test (FSIGT) have been used in other species to assess the effects of insulin on glucose homeostasis. Each of these procedures was performed on healthy cats, two weeks apart, to generate indices of insulin sensitivity - M/I (amount of glucose metabolised per unit of plasma insulin concentration) from the EGC and S(I) (insulin sensitivity) from the MMA. Close and significant correlation between M/I and S(I) in individual cats was found (r=0.91, P=0.032). Use of these research methods may further our understanding of feline diabetes mellitus and other endocrinopathies.

Decreased glucose response to insulin is maximal within 24 hours of somatotropin injection in growing pigs

Porcine somatotropin (pST) administration reduces the sensitivity of pigs to insulin, and after several days of treatment, it alters baseline circulating concentrations of pST, insulin, glucose, and other metabolites. The length of time required to develop this reduction in whole-body insulin sensitivity has not been established. To investigate this, eight castrate pigs received daily injections of either recombinant pST (120 micrograms/kg BW) or exicipient. Intravenous insulin tolerance tests (1.0 microgram/kg BW) were done before the first pST injection (Day 0) and on Day 1, 3, 5, and 8 of pST treatment. Control animals had insulin tolerance tests on Day 0 and again on Day 8 of treatment. By Day 8, the glucose response to the insulin tolerance tests in pST-treated pigs was 45% of the response of the control group (P < 0.01). Glucose response areas between Day 1, 3, 5, and 8 of pST treatment were not different (P > 0.10). The maximum effect of pST on glucose response to insulin was achieved by Day 1. Therefore, factors responsible for the development of reduced whole-body insulin sensitivity in pST-treated pigs are fully expressed within 21 hr of the initial pST treatment.

The effect of propylthiouracyl-induced low thyroid function on secretion response and action of insulin in sheep

The effect of propylthiouracyl (PTU)-induced low thyroid function on insulin responsiveness to glucose and glucose responsiveness to insulin in sheep was studied by performing hyperglycemic and euglycemic clamp experiments. All sheep were maintained at a level of 125% daily metabolizable energy intake and were housed in an environmental room that was maintained at 20 degrees C with a 16-hr lighting period. In the first study, eight female Suffolk sheep were divided equally into two groups and were subjected to oral PTU treatments of 4 mg/kg body weight (BW) per day for 7 d (low PTU) and 8 mg/kg BW per day for 14 d (high PTU). A hyperglycemic clamp experiment was conducted in each group on both control and PTU treatment periods. Plasma concentrations of triiodothyronine and thyroxine decreased (P < 0.05) in high PTU-treated sheep compared with those of low PTU-treated and control sheep. Both PTU treatments did not significantly influence basal insulin and glucose levels. Results of the hyperglycemic clamp experiment indicated that the mean plasma insulin increment and the ratio of mean plasma insulin increment to glucose infusion rate were significantly higher (P < 0.01) in high PTU-treated sheep than in low PTU-treated and control sheep. In the second study, the PTU treatment (8 mg/kg BW per day) was applied for 17 d in four male Suffolk sheep. A euglycemic clamp experiment with two insulin infusion rates (1.0 and 10.0 mU/kg per minutes) for two sequential periods of 2 hr each and thyroid hormone responses to intrajugular injection of thyrotropin-releasing hormone (1 microgram/kg BW) were performed in each sheep on both control and PTU treatment periods. In the euglycemic clamp experiment, the glucose infusion rate and the ratio of glucose infusion rate to mean plasma insulin increment were significantly reduced (P < 0.05) during the PTU treatment period for 10.0 mU/kg BW per minute of insulin infusion rate. The response areas of plasma thyroxine and triiodothyronine to thyrotropin-releasing hormone injection were blunted (P < 0.01) in PTU-treated sheep compared with those of control sheep. The high PTU treatment induced low thyroid function, enhanced insulin secretion response, and impaired insulin action in sheep.

Metabolite flux across portal-drained viscera, liver, and hindquarters of hyperinsulinemic, euglycemic beef steers

Metabolic response to i.v., exogenous insulin was characterized in three younger (355 d old, 340 kg BW) and four older (480 d old, 456 kg BW) beef steers. The steers had chronic indwelling catheters to allow measurement of blood flow and net flux of metabolites across portal-drained viscera (PDV), liver, and hindquarters (HQ). Daily N and ME intakes provided at least 1.8 times maintenance requirements. Net flux was measured before and after each steer received intramesenteric infusions of insulin, which ranged from 5 to 80 mU.h-1.kg BW-1, and intrajugular infusion of glucose to maintain euglycemia. Nonlinear fits of data provided predictions of maximal glucose entry (Rmax) for glucose infused, liver glucose release, HQ glucose uptake, and total glucose entry (TGE, sum of glucose infused plus liver release). Differences in BW could account for differences (P < .05) in Rmax for TGE between older steers (688 mmol/h) and younger steers (493 mmol/h). Plasma insulin needed to elicit half-maximal response (ED50) for TGE tended (P < .17) to be greater for older (82 mU/L) than for younger steers (49 mU/L). The decrease in liver glucose release in response to infusion of insulin was greater (P < .01) for older (-170 mmol/h) than younger (-106 mmol/h) steers. The ED50 for liver production of glucose tended (P = .13) to be greater for older (45 mU/L) than for younger (5 mU/L) steers. At 80 mU.h-1.kg BW-1, liver extraction of insulin decreased to approximately 50% of control extraction, and arterial insulin concentration was at least 9.4 times control concentrations. The PDV release and liver removal of L-lactate and propionate were not reduced by insulin infusion, although liver glucose release was 51 and 76% of control for younger and older steers, respectively. We concluded that older steers tended to be less sensitive than younger steers to the effects of insulin on glucose metabolism.

Insulin resistance, hyperglycemia, and glucosuria in intensively milk-fed calves

In intensively milk-fed calves post-prandial glucose (G) and insulin (I) concentrations, but not preprandial G concentrations, increased or failed to decrease during the growth period, compared with data from calves that were progressively weaned. This study was, therefore, designed to investigate G and I metabolism in veal calves. Euglycemic-hyperinsulinemic and hyperglycemic clamps in the unfed state demonstrated mutual responsiveness of I and G, but revealed a relative I resistance. After feed consumption, I resistance was exaggerated, as seen by decreased G clearance rates after i.v. G and I administration in fed compared with unfed calves. Milk replacer is a source of readily available lactose, fat, and protein, the intake of which, on a kilogram.75 basis, gradually increased with age. Increased substrate availability and effects of nutrients themselves were probably responsible for elevated plasma concentrations of G and I and led to I resistance. Additionally, hyperglycemia > 1.5 g/L was followed by urinary excretion of G.

Insulin responsiveness to glucose and tissue responsiveness to insulin during lactation in dairy cows

The hyperglycemic clamp and hyperinsulinemic euglycemic clamp techniques were conducted to assess insulin responsiveness to glucose and tissue responsiveness to insulin in lactating and nonlactating Holstein cows. In the hyperglycemic clamp experiment, blood glucose concentrations were clamped at 50 mg/dl above the pre-infusion values by variable rates of glucose infusion. The mean plasma insulin increments over the baseline (insulin responsiveness to glucose) during hyperglycemia were lower (P < .05) in lactating cows than in nonlactating cows (23 vs. 102 microU/ml). In the hyperinsulinemic euglycemic clamp experiment, insulin was infused at the constant rate of 6.0 mU.kgBW-1.min-1 for 2 hr, and glucose was concomitantly infused at a variable rate to maintain the pre-infusion concentrations of blood glucose. Glucose infusion rates (tissue responsiveness to insulin) were similar (3.2 mg.kgBW-1.min-1) for lactating and nonlactating cows. It is concluded that insulin responsiveness to glucose is reduced, and tissue responsiveness to insulin remains unchanged during lactation in Holstein cows.

Effect of porcine somatotropin on the response of growing pigs to acute challenges of glucose, insulin and epinephrine and during a hyperinsulinemic-euglycemic clamp

Response of tissues to homeostatic signals may play a role in the mediation of nutrient partitioning effects of somatotropin. To investigate this, the effects of exogenous porcine somatotropin (pST) on the metabolic responses to a series of intravenous challenges with dextrose, insulin and epinephrine were examined in twelve crossbred barrows (65 kg). In addition, the hyperinsulinemic-euglycemic clamp technique was used to further explore effects of pST on insulin resistance in eight of these animals. Pigs received daily sc injections of either pituitary-derived pST (120 micrograms/kg bw) or an equivalent volume of excipient for 28 d. Treatment with pST resulted in a chronic elevation of plasma glucose, insulin and non-esterified fatty acid concentrations and lowered glucagon concentrations. Acute iv challenges of dextrose (100 mg/kg bw), insulin (1.0 micrograms/kg bw), and epinephrine (2.2 micrograms/kg bw) were administered on days 21, 22, and 23 of the treatment period, respectively. Hyperinsulinemic-euglycemic clamps were carried out on day 28. Effects of pST were most dramatic for responses associated with insulin. In pST-treated pigs, insulin response to dextrose infusion was enhanced, while glucose response to insulin was attenuated and glucose clearance rate was reduced. During the hyperinsulinemic-euglycemic clamp, dextrose infusion rate required to maintain euglycemia during physiologic elevations of insulin was reduced in pST-treated pigs to 28% of control. In pST-treated pigs, glucose response to epinephrine challenge was halved, while insulin response was increased three-fold. Therefore, one mechanism by which pST shifts the nutrient partition is by altering metabolic responses to homeostatic signals. In growing pigs, this is especially evident for glucose response to insulin.